Queer theory is a field of post-structuralist critical theory that emerged in the early 1990s out of the fields of queer studies and Women's studies. Queer theory includes both queer readings of texts and the theorisation of 'queerness' itself.

Heavily influenced by the work of Gloria Anzaldúa, Eve Kosofsky Sedgwick, Judith Butler, and Lauren Berlant, queer theory builds both upon feminist challenges to the idea that gender is part of the essential self and upon gay/lesbian studies' close examination of the socially constructed nature of sexual acts and identities.

Whereas gay/lesbian studies focused its inquiries into "natural" and "unnatural"
behaviour with respect to homosexual behaviour, queer theory expands its focus to encompass any kind of sexual activity or identity that falls into normative and deviant categories.